No progress @ downloading additional components

Try boot to the Recovery Volume (command - R on a restart or hold down the option/alt key during a restart and select Recovery Volume). Run Disk Utility Verify/Repair Disk and Repair Permissions until you get no errors. Then re-install the OS. See if this will give you a good install.

OS X Recovery

OS X Recovery (2)

I am basically out of suggestions. If you are using Wi-Fi to download, see if you can attach the computer to the router using Ethernet.

If you have access to another Mac computer, if you have previously downloaded Yosemite, try downloading Yosemite from the App Store using your Apple ID. Quit the installer. You can make a bootable USB stick to install using this free program which will do all the work for you. See if you can install from that after erasing the disk.

Bootable USB Flash Drive – Diskmaker X oruse Apple’s method Create a bootable installer for OS

You might try asking an Apple Certified repair shop if it can be fixed at a reasonable cost.

Try booting into Internet Recovery (command - option/alt - R on a restart). It is a slow process. This will install the OS that the computer shipped with. You can then try to upgrade from there.

Can you reboot normally?

You may lose all your data by doing the above.

Sometimes restarting will nudge it to finish. Shut down the computer using the power button and restart.